This invention is directed to liquid ophthalmic pharmaceutical vehicles which become viscous on contacting the eye. This invention also relates to topical ophthalmic compositions comprising the vehicle and a pharmaceutically active drug.
It is known that the addition of viscous or visco-elastic polymers to an eye drop pharmaceutical composition will increase the viscosity of the composition. This is usually desirable on the premise that an increased vehicle viscosity enhances drug delivery and duration of action; see, for example, J. Pharm. Pharmacol., Vol. 34, pp. 464-466 (Jan. 7, 1982). However, it is frequently advantageous to administer ophthalmic compositions as a drop, that is, an aqueous solution or suspension rather than a thick, viscous gel or ointment which can be messy and may tend to blur vision. In addition, non-droppable compositions can present problems with patient compliance, especially with the elderly.
Another problem, in the case of suspension compositions, is their poor physical stability. Many marketed ophthalmic suspension products currently use the polymers hydroxypropyl methylcellulose, hydroxyethyl cellulose, and polyvinyl alcohol to increase the suspension's viscosity and thus decrease the settling rate of the drug particles. These suspensions are not well flocculated and, with time, the insoluble drug particles will completely settle forming a dense layer which will not resuspend easily. This in turn may undesireably lead to variable drug dosages.